Many methods have been formulated to reduce infrared radiation heatup times, especially with respect to polyester bottle preforms. Some of these methods comprise the incorporation of sufficient phosphite compounds to chemically reduce indigenous antimony compounds to their elemental state.
Other patents have provided for the addition of compounds such as iron oxides and/or anthraquinone dyes. Compounds consisting of carbon black have been added to PET to reduce the infrared heatup times of bottle preforms. U.S. Pat. Nos. 4,408,004, 4,476,272, and 4,535,118 exemplify the parameters that are necessary for the carbon black to significantly affect heatup rates. The amount of carbon black from these disclosures ranges from 0.1 to about 8 parts per million by weight based on the weight of the polyester resin. The two species of carbon black disclosed are channel black and furnace black.
One systematic problem with the use of carbon black is the concern about its fine particle size that can easily become airborne during even the slightest process upset. Another problem is the dark hue imparted to objects containing even small amounts of carbon black. Thus, the search for different effective additives other than carbon black have led applicants to the unexpected finding that graphite, a different species of carbon than carbon black, unexpectedly outperforms carbon black relative to the balance of properties required in a faster heatup polyester resin.
Thus the object of this invention is to provide a polyester resin composition which will yield aesthetically acceptable bottle preforms and which will minimize infrared radiation preform heatup time.